rt

# include <bits/stdc++.h>

# define ffor(i,name) \
	for (auto i = name.begin (); i != name.end (); ++ i)

using namespace std;

typedef long long ll;

typedef pair <int, int> pii;

int n, f[35];

int dfs (int x) {

	if (f[x])
		return f[x];

	if (x < 3)
		return f[x] = x;

	return f[x] = dfs (x - 1) + dfs (x - 2);

}

int main () {

	ios::sync_with_stdio (0);

	cin.tie (0);

	cout.tie (0);

	while (cin >> n)
		cout << dfs (n) << '\n';

	return 0;

}